Various factors affect the design of a robotic wash system. These factors include the size, shape and texture of the object or item being cleaned, the material or contaminant being removed, and whether the working fluid is recycled, contains a cleaning solvent or is heated. Robotic wash systems for small and mid size objects, such as cars, car body carriers and painting masks frequently use a wash cell or booth that encloses the item and wash system. Larger objects such as airplanes, ship cargo holds and storage tanks, frequently require a portable robot that is brought to or placed inside the object being cleaned. Some systems are designed to remove paint from the surface of the item while others are designed to remove a contaminant such as oil or grease. Some criteria allow the spray to slightly erode the item while others do not. Examples of various robotic washing and cleaning devices are discussed and shown in U.S. Pat. No. 4,817,653 to Krajicek, U.S. Pat. No. 5,038,809 to Rodgers, U.S. Pat. No. 5,358,568 to Okano, U.S. Pat. No. 5,248,341 to Berry and U.S. Pat. No. 5,454,533 to Grant, the disclosures of which are incorporated by reference herein.
Robotic wash systems include a variety of components. They typically include a robotic device and corresponding control system, a working fluid for washing the object, a pump to pressurize the fluid, nozzles to spray the fluid at the object, and an end effector or frame to support the nozzles. Detergents or other chemical solvents are usually added to the wash spray to improve cleaning effectiveness. The wash system can include a closed room or cell that contains the robotic arm, object being cleaned and working fluid spray. Wash cells help prevent work related injuries and accidents that can arise due to inadvertent contact with the rapidly moving robotic arm or its heated, pressurized spray. Wash cells also help contain the spray and its chemical that enter the air in the form of a mist or increased humidity. This helps maintain the manufacturing plant and its air supply in a desirable condition. Some examples of wash cells are described in U.S. Pat. No. 4,220,170 to Hebert, U.S. Pat. No. 4,629,409 to Satoh and U.S. Pat. No. 4,850,382 to Williams, the disclosures of which are incorporated by reference herein.
Wash systems are often designed to recycle the working fluid after it is sprayed. The sprayed fluid is typically collected and passed through one or more filters or separators to remove the contaminants and debris. Examples of some conventional recycling wash systems are described in U.S. Pat. No. 4,029,114 to Wiltrout, U.S. Pat. No. 4,652,368 to Ennis, U.S. Pat. No. 5,059,332 to Satoh, U.S. Pat. No. 5,501,741 to McMahon, U.S. Pat. No. 5,593,598 to McGinness, U.S. Pat. No. 5,665,245 to Kloss, U.S. Pat. No. 6,402,855 to Damron and RE 37,674 to Carter, the disclosures of which are incorporated herein.
Conventional robotic wash systems have difficulties cleaning contaminants such as oil and grease from an object, particularly when the working fluid is being recycled. Oil and grease can leave a thin film on the surface of the object even after it is washed. This film causes manufacturing problems when the object is being handled in other areas of the plant. Conventional wash systems add solvents and heat to help break down the oil or grease. These solvents and the increased mist and humidity due to the heat can damage the components and joints of the robotic arm. Yet, waterproofing the robotic arm is expensive and difficult to maintain. Heated working fluids also increase the rate at which biological contaminants grow in the fluid system and inside the wash cell. These biological contaminants pose a health hazard to the people working in the plant, and can damage the robotic arm and other components in the wash system.
Solvents also make it difficult to recycle the working fluid. Solvents tend to mix or otherwise combine with the water and oil or grease to create emulsions. These emulsions are difficult to filter out or separate from the water without using expensive and bulky filtration system. The oil emulsions adhere to the pipe walls and clog the nozzles and other components in the system. The emulsion build up on the pipes and components creates a resilient layer that has a dampening effect on the pressurized system. The dampening effect causes delays to pressure changes in the working fluid, such as when the system is turned on or off. The oil emulsions also attacks the pump seals and other components in the system. Economical and efficient high-pressure water pumps have seals that require the working fluid to have 5 parts per million (ppm) of oil or less to avoid frequent maintenance shut downs. The entire wash system may need to be shut down and flushed every few hundred hours to clean, refurbish or replace the piping, components and pump seals. This maintenance is expensive and can render the system unacceptable for many industrial applications where such delays adversely affect the overall efficiency of the entire manufacturing process.
Another problem with conventional wash systems is that they require large quantities of water and take up large amounts of floor space. The filters and separator in the recycling system require a significant amount of time to separate the contaminants and emulsions from the water in order to achieve the desired purity levels of the system. As a result, a large quantity of inactive water must remain in these filters and separators in order to support a relatively small volumetric flow through the spray nozzles. These filters and separators are also relatively large so that even a small wash cell requires a significant amount of plant floor space.
An additional problem with conventional robotic wash systems is that they lack the range of motion needed to use pure water to completely remove contaminants like oil from an object, particularly objects having more complex shapes. Conventional five-axis robotic arms and devices are not suitable for a pure water wash cell system. These robotic arms have difficulty positioning and articulating the spray nozzles to spray directly at or normal to the surface of the object being cleaned. The water sprays strike many surfaces of the object at angles that cannot completely remove an oil film layer. It has been found that angles of greater than about 7° degrees from normal start to deteriorate the cleaning effectiveness of a pure water spray for the purpose of removing oil and grease from the surfaces of an object. While a conventional five-axis robotic arm might be able to wash a flat tray placed in direct alignment with the robotic arm, these arms do not provide a sufficient range of motion to enable them to handle most objects. These robotic arms lack the flexibility to get into the nooks and crannies found in the vast array of items that need to be cleaned in many manufacturing settings. Items with surfaces that face in different directions or are offset from the main axis of the robotic arm, or items having a number of projections or recesses in those surfaces are particularly troublesome. Five-axis arms also have difficulty or are incapable of cleaning surfaces with small areas that must be avoided to prevent damage to sensitive components.
A further problem with conventional robotic wash systems is that they have a limited spray width. In order to clean an item with a large surface area, the robotic arm must move back and forth across a surface many times. This increases the time the robot needs to get the item through the wash cell and reduces the overall capacity of the system. While some wash systems attempt to increase the spray width by aligning a number nozzle on a bulky frame to repeatedly clean a specific object with a specific shape, these systems are not designed to handle a wide variety of item shapes and sizes found in a manufacturing setting. In addition, the bulky frame may require hundreds of nozzles to clean a large item such as an airplane.
A still further problem with an array of aligned spray nozzles is that the nozzles have to be a certain distance from the surface of the item to perform properly. Adjacent nozzles with diverging sprays tend to intersect each other so that the overall spray pattern completely covers an area in a single pass. These diverging sprays pose problems for robotic applications that manipulate the spray nozzles through several passes over an object, particularly objects with more complex shapes. The width of the diverging spray varies when the nozzle is closer to or further away from the surface being washed. When the nozzles are too close to a surface, there are gaps between adjacent sprays so that the surface is not completely cleaned. When the nozzles are too far from the surface, adjacent sprays intersect, which tends to reduce the cleaning effectiveness of the sprays. This is particularly true for a high-pressure spray system where intersecting portions of spays have significantly reduced pressure and effective cleaning power.
A still further problem with conventional wash systems is that their usefulness is limited to cleaning the item. The systems cannot be adapted to provide an additional function such as deburring the surfaces or edges of the item. Capital expenditures for another robotic cell and fluid system are needed to provide the deburring operation.
A still further problem with conventional wash systems is that the end effector is not able to remove various types of debris from the item so that the wash nozzles can clean the entire item. In a manufacturing setting, debris and garbage such as dirty rags, towels, cans, paper bags can be left on an item moving along a conveyor system leading to the wash cell. The high-pressure water jets do not produce enough volumetric flow to blow this debris off the item during the wash cycle. As a result, portions of the item may be missed. The item may need to be taken off the conveyor system downstream of the wash cell and returned for additional cleaning.
The present invention is intended to solve these and other problems.